Diabetes Forecast

Phases Of Clinical Trials in Drug Development

By Andrew Curry ,

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Once a drug has been tested in animals and found to be safe and effective, it goes through what’s known as a “clinical trial” in humans before it’s made available to consumers. These trials are usually paid for by the companies that developed them and are regulated by the Food and Drug Administration (FDA). There are four steps, or “phases,” in a clinical trial:

Phase 1

Assessing Safety

A small number of healthy volunteers, usually paid for their participation, take the drug so researchers can see if it’s safe and get a sense of how it works in the body.

Phase 2

Testing for Efficacy

Several hundred people are involved to see if the drug has an effect. Some of the study participants are given a placebo, while others are given the drug that’s being tested; researchers look to see if there’s a difference between the two groups. These are often blinded or double-blinded studies (see “Scientific Study Terms to Know,” link below). Researchers often use Phase 2 trials to determine the best dose of a drug to take into larger-scale clinical trials.

Phase 3

Testing on a Large Scale

Confirming what’s been learned in Phases 1 and 2 can involve several thousand patients, and testing often lasts for years. If results of Phase 3 are positive, drug companies can request FDA approval to begin selling the drug to patients.

Phase 4

Monitoring Patients

This phase is designed to study the long-term effects of approved drugs when they’re used in the general population and real-world settings. If a drug is bad for patients over the long term—for example, if a rare side effect emerges—it can be pulled from the market based on the results of this phase.


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Scientific Study Terms to Know



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